Latent hepatitis B virus (HBV) infection can be reactivated upon receipt of immunosuppressive therapy. The Centers for Disease Control and Prevention recommends widespread HBV screening prior to immunosuppression; however, the American Society of Clinical Oncology recommends that only select cancer patients be screened prior to chemotherapy. This controversy has hindered dissemination of screening strategies, and oncologists now face a gap in knowledge about best HBV screening practices. This has led to inconsistent screening and deleterious yet preventable clinical outcomes. We aim to study current rates of HBV screening and the comparative effect of the potential implementation of two distinct screening strategies in one of the largest Comprehensive Cancer Centers in the US. Our overall goal is to help guide oncology medical providers to achieve a higher level of clinical excellence in HBV-related patient care. The objective of this application s to determine whether widespread or selective screening is more effective in preventing reactivation of HBV infection. The central hypothesis is that widespread HBV screening is more effective than selective screening to decrease the rates of reactivation and subsequently reduce unnecessary morbidity and mortality in cancer patients. Our study will provide an evidence-based HBV screening strategy that will change the standard of HBV care for cancer patients prior to chemotherapy. Three specific aims have been designed to test the central hypothesis and accomplish the objective of this application: Aim 1: Compare patterns of HBV screening before and after the release of recommendations from the Centers for Disease Control and Prevention and from the American Society of Clinical Oncology. Aim 2: Assess the impact of widespread vs. selective screening of cancer patients undergoing chemotherapy on the ability to detect prevalence of HBV infection, incidence of reactivation, and delays in cancer therapy. Aim 3: Develop a decision-analysis model to compare the predictive ability and cost-effectiveness of implementing widespread vs. selective HBV screening. This R21 application will establish the current status of HBV screening and infection, and burden of reactivation; the adherence to national screening guidelines; and the potential implementation of two distinct screening strategies. Through a decision-making processes, we will determine whether widespread or selective HBV screening is the most effective screening strategy for cancer patients. This application possesses the potential to shift the standard of care for cancer patients with HBV prior to chemotherapy.